Acids & Bases Flashcards
What are the 3 physical properties of acids?
- Acids taste sour
- Dilute acids are irritants and will result in rashes and blisters
- Acids turn blue litmus paper red
What makes a compound/substance an acid?
If it dissociates H+ ions when dissolved in water
Acid + Metal ——> ?
Salt + H2
Acid + Base ——> ?
Salt + H2O
Acid + Metal carbonate ——> ?
Salt + H2O + CO2
What type of reaction is this? Acid + Base ——> Salt + H2O
Neutralisation reaction
How do you differentiate between strong acids and weak acids? Give an example of a strong and weak acid.
Strong acids have the ability to dissociate fully in water to produce a high concentration of H+ ions. Weak acids only have the ability to dissociate partially in water to produce a low concentration of H+ ions. Hydrochloric acid is a strong acid while hydrofluoric acid is a weak acid.
Explain concentration of an acid.
- Concentration of acid is dependent on how diluted the solution is (the dilution factor)
- Concentration refers to number of acid molecules present per water molecule
- Usually expressed in mol/dm-3
What is basicity of an acid?
The basicity of an acid depends on the acid’s chemical formula. Basicity refers to number of H+ ions produced per molecule. For example, HCl produces 1 H+ ion and is monobasic, H2SO4 produces 2 H+ ions and is dibasic, H3PO4 produces 3 H+ ions and is tribasic
Can a strong acid have a low concentration of H+ ions?
Yes, use a strong acid like nitric acid and add a large amount of water to it.
If we dissolve 2 strong acids, nitric acid and sulfuric acid, in water, which one will produce a higher concentration of H+ ions?
Even though both strong acids will dissociate fully in water, sulfuric acid would produce a higher concentration of H+ ions. Sulfuric acid is dibasic, producing 2 H+ ions per molecule while nitric acid is monobasic, producing only 1 H+ ion per molecule.
What is a base?
A base is defined as a substance which reacts with an acid to form a salt and water only. All metal oxides and hydroxides are bases.
What are alkalis?
Alkalis are a special group of bases that are soluble in water. Hence, alkalis dissociate either fully or partially in water to produce OH- ions, giving rise to its alkaline properties. In other words, alkalis are a subset of base.
The oxides and hydroxides of metals in which 2 groups of the periodic table form alkalis?
Group l and Group II
Name the 4 physical properties of alkalis
- Alkalis taste bitter
- Dilute alkalis feel slippery and soapy to touch
- Concentrated alkalis are caustic, causing chemical burns
- Alkalis turn red litmus paper blue
What makes a compound/substance an alkali?
A compound is considered an alkali when it dissociates OH- ions when it dissolves in water.
What is a weak alkali?
A weak alkali is one that only dissociates partially in water to produce a low concentration of OH- ions.
What must you take note of when writing the dissociation reaction for a weak alkali or acid? And why?
- Must write the reversible sign ⇌. Since it is a weak alkali, some of the ions may turn back to the atom.
- A commonly used weak alkali is aqueous ammonia. Dissociation reaction for ammonia is NH3 + H2O ⇌ NH₄⁺ + OH-. Some NH₄⁺ ions turn back to NH3, resulting in low concentration of OH- ions produced.
What are the 4 uses of alkalis?
- Toothpaste to neutralise acid on teeth
- Calcium hydroxide used to neutralise acidity in soil
- Magnesium hydroxide in indigestion tablets, aka antacid pills
- Sodium hydroxide in floor & cleaners
Alkali + Ammonium salt ——> ?
Salt + H2O + NH3 (g)
Why must litmus paper be moist when testing for ammonia gas?
Moist litmus paper must be used in order for the ammonia gas to dissolve in water and dissociate to form OH- ions.
If HCl (aq) is hydrochloric acid, does this mean HCl (l) which is hydrogen chloride, an acid as well?
No. An acid is only considered as an acid after it has dissociated in water and H+ ions are formed. This is the same for alkali. An alkali is only an alkali after it has dissociated in water and formed OH- ions.
What must you remember when writing dissociation reaction for weak alkalis?
Must add water. For example, write NH3 + H2O ⇌ NH₄⁺ + OH- and not NH3 ⇌ NH₄⁺ + OH-.
The pH scale ranges from 0 to 14. pH 7 is considered neutral. pH 14 is considered very _____ and ph 1 is considered very _____.
Alkaline; acidic
The indicator methyl orange is _____ when acidic, _____ when neutral and _____ alkaline.
Red; orange; yellow
The indicator screened methyl orange is _____ when acidic, _____ when neutral and _____ alkaline.
Purple; grey; green
The indicator phenolphthalein is _____ when acidic, _____ when neutral and _____ alkaline.
Colourless; pale pink; pink
The indicator bromothymol blue is _____ when acidic, _____ when neutral and _____ alkaline.
Yellow; green; blue
